FAMOS (Floating gate avalanche injection metal-oxide-semiconductor), SAMOS (Stacked gate avalanche injection metal-oxide-semiconductor), MNOS (Metal nitride oxide semiconductor) and 1-Transistor Cell (one transistor and one capacitance per cell) were developed in the prior art as semiconductor elements which allow change of the information written therein.
A FAMOS element provides, as disclosed in "Solid State Electronics", Vol. 17, page 517, 1974, a floating gate which is surrounded by a silicon dioxide SiO.sub.2 material, wherein information is written by injecting electric charges and the charges injected thereinto are maintained in the floating gate. SAMOS provides another gate which is added to the structure of FAMOS. Such a gate is arranged on an insulating layer which is on the floating gate of the FAMOS element so as to facilitate the injection of charges into the floating gate. Information which is written in FAMOS can be erased by irradiation with ultraviolet rays. MNOS provides a silicon nitride layer (Si.sub.3 N.sub.4) on a dielectric insulating layer (SiO.sub.2) and a metal layer which is arranged on the silicon nitride layer, so as to form a charge trap layer between the dielectric insulating layer (SiO.sub.2) and the silicon nitride layer (Si.sub.3 N.sub.4). This charge trap layer has a function similar to that of the above-mentioned floating gate, that is, electric charges are injected into the charge trap layer. The so-called 1-Transistor Cell element comprises a transistor and a storage capacitor. Information is written in the storage capacitor by switching the transistor on and the information is stored therein by switching the transistor.
In the structures of FAMOS, SAMOS, and MNOS, the gate electrode should be enclosed by the insulating substance, or the insulating substance under the gate electrode should have a multilayer or a double layer construction. Therefore, the construction of each of these elements is complex, and the manufacturing of these elements is troublesome if compared to the manufacturing MOSFET (Metal-oxide-semiconductor field effect transistor).
In a 1-Transistor Cell, a capacitor is required in addition to a transistor for constructing a cell. Furthermore, when 1-Transistor Cells are used in an LSI (large scale integrated circuit), a highly sensitive amplifier is required because of the bit-line capacitance problem.